This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-270480, filed Sep. 6, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device for displaying an image in a combination manner of light reflection and light transmission.
2. Description of the Related Art
Conventionally, a display device for a portable terminal such as a mobile phone, pocket pager or the like, has been used for the purpose of displaying simple characters such as numerals, characters or the like. With the recent remarkable progress in the information technology, a small, light and thin display device capable of displaying a high-resolution color image at low power consumption is required for the portable terminal.
Active matrix liquid crystal display devices of a reflection type, for example, are regarded as those which are most likely to comply with such a requirement. Some of the display devices have been brought into practical use. Such a display device can display a clear image in daylight, without requiring an internal light source. However, when the image is displayed in the darkness of night, it can hardly be recognized. Thus, the use of the display device tends to be limited by its environment.
As a countermeasure for the problem, a front light technique has been proposed. In this technique, a display surface of the reflection-type liquid crystal display device is covered with a transparent plane light source which supplements an illuminance of an external light. The plane light source does not require any modification of the internal structure of the liquid crystal display device, but it causes a decreased luminance of the reflected light, a blur of the image, an increased depth of the image, or the like which impairs the image quality.
Under the circumstance described above, Jpn. Pat. Appln. KOKAI Publication No. 11-316382 discloses a liquid crystal display device which displays an image in a combination manner of light reflection and light transmission. In this liquid crystal display device, each pixel electrode is configured in a combination of a conductive light reflective film and a conductive light transmissive film. The conductive light reflective film reflects external light so that the image can be displayed in a light reflection manner under a high-illumination environment such as outdoors in daylight, and the conductive light transmissive film transmits a light from a backlight so that the image can be displayed in a light transmission manner under a low-illumination environment such as the darkness of night.
However, individual processes are used for forming the light reflective and light transmissive films of predetermined patterns. This causes a decrease in the manufacturing yield and an increase in the manufacturing costs. In addition, there is another problem that a bright image can hardly be obtained since the reflection efficiency is lowered due to an overlap of the light reflective film and the light transmissive film.
An object of the present invention is to provide a liquid crystal display device which can prevent the reflection efficiency from being lowered without requiring complicated manufacturing processes.
According to the invention, there is provided a liquid crystal display device which displays an image in a combination manner of light reflection and light transmission, the device comprising: a first electrode substrate including a plurality of pixel electrodes; a second electrode substrate including a counter electrode facing the plurality of pixel electrodes; and a liquid crystal layer held between the first and second electrode substrates, for modulating reflected light and transmitted light for pixels each defined by a corresponding pixel electrode, wherein each pixel electrode includes a conductive light reflective film for reflecting incident light and at least one opening formed as a missing portion of the conductive light reflective for transmitting incident light.
In the liquid crystal display device, each pixel electrode includes a conductive light reflective film for reflecting incident light and at least one opening formed as a missing portion of the conductive light reflective film for transmitting incident light. Since the opening can be obtained together with the conductive light reflective film by a patterning process of forming the conductive light reflective film into a predetermined pattern, no complicated manufacturing process is required. Furthermore, since the opening allows transmission of incident light, there is no need to provide a conductive light transmissive film such as an indium tin oxide (ITO) which overlaps the conductive light reflective film and decreases the reflection efficiency. Hence, the liquid crystal display device can display a brighter high-resolution image in combination of reflected light and transmitted light. Furthermore, the device can be manufactured at a low cost.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.